1. Field of the Invention:
This invention relates generally to waste tank servicing assemblies, and more particularly relates to an automatic hydraulic valve control apparatus for use in combination with a lavatory waste tank adapted to be installed in a vehicle, such as an aircraft.
2. Description of the Prior Art:
Most aircraft lavatory systems include a waste tank which may be used with a recirculating toilet system. The tank retains human wastes, and is drained by service personnel on the ground. During this process, service personnel connect the tank with a fluid pressure line for providing a rinsing fluid while the tank is draining, and for providing a given amount of fluid as a pre-charge of the tank. The pre-charge is necessary for operation of a recirculating toilet system. In most conventional systems, the service personnel normally operate a drain valve separately from the fluid pressure charging of the tank, so that occasionally the service personnel allow the tank to rinse and drain for excessive periods of time, wasting the cleaning or other fluid being used. After the drain valve is closed, fluid is to be allowed to continue to flow for a short period of time to provide the precharge volume of fluid for the tank. Service personnel occasionally allow the fluid charging to continue until the tank overflows, causing corrosion in the flooded portions of the aircraft.
Various electronically controlled automatic toilet tank servicing systems have been devised, utilizing electronically timed solenoid valves for controlling draining time and pre-charge time. However, such systems are not generally completely automatic, and require supervision by service personnel to manually open a stuck drain valve to prevent overflow of the tank. Such systems also typically include a flow meter, electronic counters, and battery packs to power the electronic system. Another type of automatic toilet tank servicing system provides a pre-charge tank which is filled when the system is charged with fluid pressure, opening the drain valve and rinsing the tank. When the fill line is depressurized, the drain valve is closed by the operation of the hydraulic system, and the pre-charged tank then discharges its contents to the tank rinse line thereby providing the tank with a given amount of pre-charge fluid. Such a system is shown in U.S. Pat. No. 4,584,726, but is also not completely automatic, requiring supervision by a technician to depressurize the system to commence the pre-charge of the tank, so that it is possible for a technician to rinse the tank for an excessive period of time. The system also requires close supervision by a technician to manually open the drain valve if it is stuck, in order to avoid a potential overflow of the system. In addition, the pre-charge tank of this system occupies an additional volume of space which cannot be accommodated in the lavatories of most passenger aircraft. Finally, the charging line of the tank may also siphon fluid from the system, further wasting fluid, and adding to the possibility of corrosion. Fill lines of conventional systems generally have check valves to prevent siphoning. These check valves also typically have small vent holes to allow draining of the fill lines following servicing on the ground, in order to prevent freezing of fluid in the lines at high altitudes. However, these vent holes effectively defeat the purpose of the check valve at the low atmospheric pressures of high altitude flight.
Ideally, an automatic toilet tank system should not require close supervision of the drain valve to insure that the system does not overflow or of the period of time in which the tank is rinsing while it is being service. Ideally, such a system should operate automatically to cycle through the draining, rinsing and pre-charging of the tank once the technician connects the fluid pressure charging line to the fill line of the system. It would also be ideal for such a system to prevent siphoning of fluid from the the tank through the fill lines of the system when the fill line port is exposed to high vacuum at an aircraft's high cruise altitudes.